In the environment of a Telephone Central Office, voice and digital data are received from nearby telephone service subscribers and processed before transmission over a transmission medium to distant telephone subscribers. Similarly, voice and digital data are also received from distant telephone subscribers and processed before delivering the data to the nearby subscriber. For obvious reasons, the nearby subscriber is commonly called "near side," and the distant subscriber is commonly called "far side" or "long haul" by those in the telecommunication industry. Presently, near side data is received in DS1, and data is transmitted on the DS3 level. By convention, DS1 is composed of 24 DS0 channels, and DS3 is composed of 28 DS1 lines.
The data processing which takes place inside the Telephone Central Office includes echo canceling, DS1-to-DS3 multiplexing and performance monitoring. Presently, each function is performed by a separate piece of equipment, typically called an echo canceler, a multiplexor and a performance monitor. The three pieces of equipment are physically installed in separate mounting racks possibly in different parts of the Telephone Central Office. In addition, each piece of equipment also requires a separate power supply and a video display terminal.
Referring to FIG. 1, a block diagram illustrating the conventional setup is shown. An echo canceler 10 and its control module 12 are coupled to the near side via a cable which is coupled to a DSX-1 (Digital Signal Cross-Connect-1) 16 on a patch panel. DSX-1 16 is a location where jumper wires are used to "patch" together two cables carrying DS1 level signals. Echo canceler 10 further receives and sends control information to a Central Office computer and also produces an alarm in the event of abnormal operations. Echo canceler 10 is coupled to a performance monitor 18 and its control module 20 via cables 22 and another DSX-1 24. Typically, cables 22 may have a combined length of 100-200 feet. Performance monitor 18 is also coupled to a Central Office computer and additionally produces an alarm indicative of faulty operations.
Performance monitor 18 is further coupled to a M13 multiplex-demultiplexor (Ml3 muldem) 26 and its control module 28 via cables 30 which are patched together at a DSX-1 32 on the patch panel. Similarly, it is not uncommon for cables 30 to have a total length of 100-200 feet. M13 muldem 26 also sends and receives control information to and from the Central Office computer. Additionally, M13 muldem 26 is also capable of generating an alarm in the event of faulty operations. M13 muldem 26 is coupled to the far side via a cable 34 and a DSX-3 36, which transmits DS3 level signals.
Echo canceler 10, performance monitor 18 and M13 muldem 26 are all commercially available. For example, a commercially available echo canceler EC7600-M2 is manufactured by DSC Communications Corporation. Performance monitoring at the DS0 level may be implemented with Network Characterization System (NCS) manufactured by DSC Communications Corporation or Monitor 2400 manufactured by Compression Telecommunication. DS1 level performance monitoring may be performed by Network Channel Office Equipment (NCOE) manufactured by Tautron, which is a subsidiary of General Signal Corporation. DS1-to-DS3 multiplex-demultiplexors are available from DSC Communications Corporation under the name TM45000 and many other manufacturers.
The setup as shown in FIG. 1 is prone to errors due to the cabling and patching between the three components. For example, misplacement of the jumper wires that patch two cables together and incorrect cable installation can cause errors. Furthermore, bit errors may be caused by electromagnetic interference on the long cables and cables which are not terminated properly. The cables may not be terminated properly due to improper impedance matching in the DSX or failure to provide the correct line buildout network (not shown) for the length of the cable used. With the increasing number of telephone service subscribers, more consideration must be given to the amount of space required to house the equipment and the availability of DSX ports along with the overall power consumption and cost of the equipment.
Furthermore, the Performance Monitoring equipment 18 is usually used to monitor DS1 level parameters on both sides of the device. When used in conjunction with echo canceler 10 as shown in FIG. the DS- signal being monitored on the echo canceler side is purely intra-office and the monitoring is thus not so valuable. On the other side, the DS1 signal that is monitored is part of the facility, albeit embedded in a DS3, and monitoring does provide significant value. Therefore, it is desirable to provide for an apparatus which can monitor the DS1 signals including the embedded DS1 signal in the DS3, the equivalent of the signal carried in cables 30, and the DS1 signal carried in cables 14.
In the system shown in FIG. 1, separate control ports and alarm ports are required for each piece of equipment. Furthermore, as each piece of equipment is coupled to a separate operator interface in the form of a video display terminal, an operator must be familiar with three different command languages and three sets of screen layouts in order to communicate with all three pieces of equipment. This adds to the complexity of the system needlessly, and is likely to create confusion for the operator.
Therefore, it is desirable to provide a more compact system which performs the echo canceling, performance monitoring and M13 multiplexing-demultiplexing tasks and yet eliminates possible errors arising from having interconnecting cables.